[PATCH qemu-server v5 10/13] network: sdn: push the DHCP mappings of a guest when it resumes

[Hannes Laimer <h.laimer@proxmox.com>]

A mapping edit and a migration of the guest exclude each other, but
an edit through a node not yet upgraded takes no lock and writes no
reservation, so it can land while the guest is migrated. Every resume
now pushes the mapping of each NIC of the guest on the local node
before the guest continues, and the last step of a live migration
resumes the target after the config moved, so the target serves what
the cache vouches for. The push asks the IPAM only when the cache
cannot vouch for the address. A busy reservation lock is not waited
for, since the push holding it writes the line as well. An IPAM that
does not answer then holds the resume up to the request's timeout,
and the migration task fails naming the resume. That beats serving
the guest a stale address.

Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
---
 src/PVE/QemuServer/Network.pm  | 17 +++++++++++++++++
 src/PVE/QemuServer/RunState.pm |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/src/PVE/QemuServer/Network.pm b/src/PVE/QemuServer/Network.pm
index b4893c015646..59b21fcfb055 100644
--- a/src/PVE/QemuServer/Network.pm
+++ b/src/PVE/QemuServer/Network.pm
@@ -272,6 +272,23 @@ sub add_random_macs {
     }
 }
 
+# a resume pushes the current mapping of each NIC. The target of a live
+# migration resumes after the config moved and serves the current addresses
+# from then on. The push does not wait for a busy reservation lock, the push
+# holding it writes the line as well
+sub add_nets_dhcp_mapping {
+    my ($conf) = @_;
+
+    for my $opt (keys %$conf) {
+        next if $opt !~ m/^net\d+$/;
+        my $net = parse_net($conf->{$opt}, 1) or next;
+        next if !$net->{bridge} || !$net->{macaddr};
+        # a resume does not fail on its DHCP backend
+        eval { PVE::Network::SDN::Dhcp::update_mapping($net->{bridge}, $net->{macaddr}, 1) };
+        warn $@ if $@;
+    }
+}
+
 sub add_nets_bridge_fdb {
     my ($conf, $vmid) = @_;
 
diff --git a/src/PVE/QemuServer/RunState.pm b/src/PVE/QemuServer/RunState.pm
index 889ddd28287b..828d79159e90 100644
--- a/src/PVE/QemuServer/RunState.pm
+++ b/src/PVE/QemuServer/RunState.pm
@@ -181,6 +181,8 @@ sub vm_resume($vmid, $skiplock = undef, $nocheck = undef) {
 
             PVE::QemuServer::Network::add_nets_bridge_fdb($conf, $vmid)
                 if $resume_cmd eq 'cont';
+            PVE::QemuServer::Network::add_nets_dhcp_mapping($conf)
+                if $resume_cmd eq 'cont';
 
             mon_cmd($vmid, $resume_cmd);
         },
-- 
2.47.3